Telephone-exchange system



Oct. 16 1923.

S. B. WILLIAMS, JR

TELEPHONE EXCHANGE SYSTEM Filed Nov. 25 1919 4 Sheets-Sheet 2 W F Nma/enior Oct, 16 1923. 1,471,017

5. B. WILLIAMS, JR

TELEPHONE EXCHANGE SYSTEM 7 Filed Nov. 25. 1919 4 Sheets-Sheet a 4y 7Any Get. 1.6 1923.

S. B. WILLIAMS, JR

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UNITED STATES PATENT OFFICE,

SAMUEL B. WILLIAMS, JR, OF BROOKLYN, NEW YORK, ASSIGNOR '10 WESTIERNiELEC- TRIC COMPANY, INCORPORATED, OF'NEW YORK, N. Y., .A. CORPORATIONOF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed November 25, 1919. Serial No. 840.542.

To all whom it may concern Be it known that I. SAMUEL B. WILLIAMS,

Jr.-, a citizen of the United States, residing at Brooklyn, in thecounty of Kings, State of New York, have invented certain new and usefulImprovements in Telephone-Exchange Systems, of which the following is afull, clear, concise, and exact description.

This invention relates to telephone exno change systems employingmachine switch ing, and more particularly to private branchinstallations wherein connections may be made between stations withinthe private branch installation, or between'such stations 1 and acentral ofiice.

In many business houses where the greater part of the calls are madebetween substations within the private branch exchange, the number ofcentral ofiice calls is not sulficient to occupy the full time of anoperator. It is, however, desirable to have provision made for answeringincoming central oifice calls, for iving information to persons callingWitlilIl the branch exchange, and for supervising certain outgoingcentral ofiice calls. Toprovide such service has in the past requiredeither a switchboard and operator at the branch exchange or else a fargreater number of central oflice trunk circuits than the number of callsbetween branch exchange stations and central ofiice stat-ions warranted.

It is the object of this invention to pro vide such serviceat the branchexchange without either a full time operator or an unnecessarily largenumber of central ofiice trunk circuits.

According to one feature of the invention one or more substationshereinafter termed receiving stations, having no special equipment, aredesignated to provide operator service. These substations may be thoseof certain clerks whose incidental duty it is to answer calls eitherfrom the central ofiice or from stations within the branch exchange wheninformation is desired. Inasmuch as it requires only a small portion ofthe time of one of these clerks and as she need have no specialequipment other than an ordiiary telephone subset provided with a simplecal ing device, it is possible without undue expense to have anintelligent personanswer incoming central oflice calls, which is a greatadvantage to a business.

According to another feature of the invention a trunk circuit isprovided which terminates in four places, namely an operators positionat the central ofiice, a nonnumerical switch having access to receivingstations, the bank termlnals of branch exchange final selector switchesand the brushes of companion final selector switches at the branchexchange.

Still another feature of the invention is y the provision of a trunkcircuit terminating in only three of the previously named points, allwithin the branch exchange, namely, a non-numerical switch having accessto receiving stations, the bank contacts of final selector switches andthe brushes of companion final selector switches.

Referring to the drawings, Figs. 1, 2 and 3, with Fig. 2 to the right ofFig. 1 and Fig. 3 above Fig. 2, show diagrammatically the c1rcu1t-semployed in completing connections between various substations withinthe branch exchange and between such stations and a central ofiice.

Fig. 4 shows partly schematically and partly diagrammatically all thepossible types of connections in this systemwhen the number of branchexchange substations is small; and Fig. 5 is a simplified diagram of theconnections in a system of this character when the number of branchexchange substations is great enough to re uire the use of firstselector switches in addition to final selector switches.

To the left of the dotted line in Fi .1, a substation ,A and a linefinder switc 100 with circuits therefor are shown. In the dottedleft-hand lower corner of Fig. 1 are shown relays individual to thegroup of line finders which have access to the substation A. To theright of the dotted line in Fig. 1 and to the left of the dotted line inFig. 2, is shown a final selector switch 200 with the three types ofcircuit terminals on which it may be set. To the right of the dottedline in Fig. 2 isa trunk circuit linking the final selector terminalswith a nonnumerical or hunting switch 25 and a comnumber of lines in theexchange.

panion final selector switch 20. In Fig. 3 is another trunk circuitsimilar to the one in Fig. 2, but also leading to multiple jacks at acentral office, one of which is indicated within the dotted rectangle.

Figs. 6 and 7 represent a detail of the circuit of Fig. 1 and show thealternate connections of the cut-off relay. Fig. 6 represents theconnection when the associated line is a restricted service line andFig. 7 represents the connection when the service of the associated lineis not restricted.

The receiving station F shown in Fig. 3 is provided with a cordlessboard but it will be apparent from the description hereinafter that itperforms no function which may not be done just as well by a stationsuch as E.

The structure of the line finder, final se lector, and companion finalselector switches may be of the type fully disclosed in the patent toForsberg No. 1,252,420 of January 8, 1918, but it IS understood thatthese switches might be of any well known type.

In Fig. 4 are shown banks of terminals divided into levels 400, 401,402, 403 and 404 to which substations A, B, C, D and receiving stationsE and F are connected. Additional levels of bank terminals, not shown,may be provided in accordance with the Each heavy dot, 31, 32 representsa set of terminals and each line 405, 406 represents a set of conductorsmaking up trunk circuit.

. Line finder switches 100, final selector switches 200, and two kindsof companion final selector switches 20 and 300 are arranged to engagewith their brush sets one of the multiple terminal sets of any line inany level. Non-numerical or hunting switches 25 and 30 are arranged tohunt over the level 402 which leads to receiving stations E and F.

It willthus be seen that any subscriber may by initiating a call havehis line picked up by a line finder 100. By operating his calling devicehe may set a final selector 200 in its primary movement so that one ofits brush sets 407 or 408 will be ready to travel over a group ofterminals in any level of the bank. If he has chosen a level 402, 403 or404 he may then direct the switch 200 in its secondary movement to anyline in that level when a call will be complete to the wantedsubscriber. If the subscriber sets the final switch 200 in its primarymovement on level 400 it will in its secondary movement hunt an idlecentral office trunk 406. If he has chosen level 401, however, theswitch 200 will in its secondary movement automatically select an idletrunk 405 and the hunting switch 25 will select an idle receivingstation E or F. If the calling subscriber desires the call extended, thereceiving subscriber operates his calling de vice to set the companionfinal se ector switch 20 on any desired level of terminals. The switch20 may be set directively on the terminals of any station in the branchexchange, or it may be directed in its primary movement to the centraloflice level 400, when in its secondary movement it will antomaticallyselect an idle trunk 406.

Provision is made for restricting certain substations to interior calls,so that if a subscriber at one of these stations should set a finalselector 200 on level 400, a connection would be completed throughauxiliary brush 201 and the commutator segment 202, individual to thecentral ofilce level, to restore the switch. All subscribers may haveunrestricted connection with a receiving station however, and thereceiving subscriber may at his discretion extend such connectionseither within the exchange or to the central office.

Incoming calls from the central oflice go 'over the trunk circuit shownin Fig. 3 to a hunting switch 30 which connects them with an idlereceiving station F. The receiving subscriber having inquired and foundout what is wanted, may then set the companion final selector switch 300to complete the connection with a desired substation. As soon as thecompanion final selector switch is set the switch 30 is restored tonormal leaving the receiving station ready for the next call.

In Fig. 5 are shown the possible connections in a branch exchangeemploying both first and final selector switches. Either an ordinarysubstation A or a receiving station E will, upon the initiation of acall, be seized by a line finder 100 and connected to a first selector500. The subscriber, by operating his calling device then sets theselector 500 in its primary movement on either a level 401 leading to atrunk circuit such as that shown in Fig. 2, a level 400 leading to atrunk circuit such as that shown in Fig. 3, or on the particular level501 leading to final selectors 200 in whose banks are terminals of thewanted line. If he has chosen a level 501, an idle final selector 200 isautomatically selected in the secondary movement of the switch 500. Byoperating his calling device the subscriber may then directively controlthe final selector 200 in both its primary and secondary movements tocomplete a connection with the wanted subscribers line within the branchexchange. If he has chosen a level 400, the selector 500 will in itssecondary movement select an idle gunk circuit 406 leading to thecentral of- If the subscriber A sets the first selector 500 on level401, an idle trunk circuit 405 will be selected in the secondarymovement of the switch 500,. whereupon a hunting switch 25 will pick outan idle receiving subscriber E. The receiving subscriber by operatinghis calling device may then set another first selector 500 on either ofthe three levels 501, 400 or 401. If the switch 500 is set on a level501, the connection will be completed to any wanted substation withinthe exchange through a final selector switch 200 in the same manner aswhen the calling subscriber made such a call without-the intervention ofa receiving subscriber. When the switch 200 has been set the huntingswitch 25 releases to leave the receiving subscriberxready for the nextcall.

Calls coming in from the central office cause a hunting switch 30 toselect the line of an idle receiving subscriber E who answers the call.Having found that an extension of the connection is desired he operateshis calling device to set the first selector switch500 on terminal 501and then re-opcrates the calling device .to set switch 200 on theterminals of the wanted subscribers line. The hunting switch 30 releasesas soon as the switch 200 is set.

Having described the general circuit arrangements it is believed thatthe invention will be readily understood from a detailed description ofthe setting up of the various possible connections.

I m'tz'atz'o'n; of a call by a private branch ea:- change .mbscm'bcr andthe primary settz'ng of the final selector switch.

When the subscriber at A lifts his receiver off the hook he operates aline relay 101 over a circuit from grounded battery, right-hand windingof relay 101, back contact and inner armature of relay 114, conductor115, substation A, outer armature and back contact of relay 114,left-hand winding of relay 101 to ground. Relay 101 in attracting itsleft-hand armature creates a calling condition upon the multiple 116 ofsubstation A in the finders in which such line appears. In attractingits right-hand armature, relay 101 completes a circuit from ground, itsright-hand armature and front contact, conductor 104, back contact andarmature of relay 102, through the winding of relay 103 to groundedbattery. Relay 103 is energized in this circuit, and locked up fromgrounded battery through its winding, front contact and left-handarmature over the circuit previously traced. Relay 103, in energizing,places a ground on commutator segment 105 individual to the group oflines of which substation A is a member. A circuit is now completed fromgrounded battery, righthand winding of release control relay 120,conductor 121, side switch arms 122 and 123, first position, conductors124, 109 and 108, back contact and left-hand armature of relay 107,conductor 106 to ground at the right-hand armature and front contact ofrelay 103. Rela I 120 is energized in this circuit and is 100 ed up overa circuit from grounded battery through the right-hand winding, armatureand front contact of relay 120 over conductor 108 and the circuit justtraced to ground at the right-hand armature of relay 103. A circuit isalso completed from ground, front contact and right-hand armature ofrelay 103, conductor 106, left-hand armature and back contact of relay107, conductor 108, conductor 109, side switch arms 110 and 111, firstposition, back contact and arma ure of magnet 112 through the winding ofprimary magnet 112 to grounded battery. Primary magnet 112 interruptsits circuit and steps the brushes 117, 118 and 119 around until thegroup of lines containin station A is reached. When the finder brus esreach the group in which the call originated, a circuit is completedfrom ground, spring 125, commutator segment 105, brush 113, conductor126, back contact and right-hand armature of relay 107, side switch arm127, first position, conductor 128 through the windings of theslowto-release escape magnet 129 and slow-torelease primary magnet 112to grounded battery. Magnet 129 is shunted at this time by ground at thearmature of primary magnet 112, but when this armature opens near theend of the step, magnet 129 is energized to advance the finder sideswitch to position 2. The circuit for primary magnet 112 is now brokenat side switch arm 111 and the switch stops with a brush set in positionto traverse the calling group of lines.

Magnet 129 is held energized in position 2 of the side switch over acircuitleading from grounded battery, winding magnet 11.2. windingmagnet 129, conductor 128, side switch arm 127, second position, backcontact and armature of relay 130 to ground; but magnet 112 is marginaland will not en-- ergize in this circuit. A circuit is now completedfrom grounded battery, winding of secondary magnet 131, armature andback contact of this magnet, conductor 132, inner left-hand armature andfront contact of relay 120, side switch arms 123 and 122, secondposition, conductor 128 in parallel with the circuit for magnet 129previously traced to ground at the back contact and armature of relay130.

Secondary magnet 131 in energizing interrupts its circuit and steps thebrushes 117 118 and 119 to the terminals 116, 133 and 134 of the callingline. \Vhen this line is reached a circuit is completed from groundedbattery, resistance 135, front contact and left-hand armature of relay101, conductor 136, terminal 116, brush 117 side switch arms 111 and110, second position. through the windingof relay--to ground. Relay ofrelay &

previously traced for escape magnet 129. This magnet in releasing passesthe side switch arms into position 3.

In position 3 of the side switch the cut-off relay 114 is operated overa circuit from grounded battery through the left or both windings ofrelay 114 (see Figs. 6 and 7), according as the line A is a restrictedor a non-restricted line as will appear more fully hereinafter, terminal116, brush 117, side switch arms 111 and 110, third position, throughthe winding of relay 196 to ground. Relay 114 in energizing opens thecircuit of line rela 101; Relay 101 in retracting its left-han armatureremoves the calling condition from the terminals 116 of the line A, andin retracting its right-hand armature it breaks the circuit of relay 103which thereupon is deenergized. The circuit for relay 102 is broken atthe right-hand armature oi relay 103, and the line finder startingrelays are ready forthe next call.

In position 3 of the side switch a circuit is also completed forstepping rela 137 from grounded battery, left-hand winding of saidrelay, side switch arms 123 and 122 third position, conductors 138 and139, brush 118, terminal 133 through the apparatus at substation A,terminal 134, brush 119, conductors 140 and 141, side switch arm 142,conductor 143, right-hand winding of relay 137 to ground. Relay 137 inbeing energized completes a circuit for slow-to-release relay 150, fromgrounded battery, winding 150, front contact and armature of relay 137,through primary off-normal spring 151 to ground. Relay 150 in attractingits right-hand armature completes a circuit from ground, right-handarmature and front contact of rela 150, conductor 157, back contact and1e -hand armature of slow-to-release release magnet 158, conductor 159,contact spring 160 of relay 145, conductor 161 throu h the righthandwinding of relay 162, si e switch arm 163, first position, lefthandwindin of rela 162 to grounded battery. Circuits are a so completed atthis time from grounded battery through the right-hand winding of relay107, and from rounded battery through the lefthand winding of relay 120in parallel with the circuit just traced, to ground at the righthandarmature of relay 150. Relays 162 and 107 are energized in thesecircuits, and relay 120 is held up after its locking circuit is brokendue to the energization of relay 107. Relay 107, in being energized,connects the in-starter wire 164 over conductor 106 to the out-starterwire 165, to permit operation of other line finders in the group towhich the finder 100 belongs.

The calling subscriber now receives a distinctive dial tone over acircuit which ma be traced from ground through the secon ary winding 144of tone source D. T. outermost right-hand armature and back contact ofrelay 145, side switch arm 146, first position, conductor 14?,condensers 148 and 149, side switch arm 122, third position, thence inparallel with the circuit of relay 137 over the talking conductors,through the substation apparatus and back over the talking conductorsthrough the right-hand winding of relay 137 to ground. The subscriber,hearing this tone, now operates his sender S to transmit the first digitof the wanted number. In returning to normal the sender interrupts thecircuit of the stepping relay 137 a number of times corresponding to thedigit involved. Each time relay 137 retracts its armature, a circuit iscompleted from ground primary oil-normal spring 151, armature and backcontact of relay 137, lefthand armature and front contact of relay 150,side switch arm 152, third position, conductor 153, through the windingof slow-torelease relay 1 54, conductor 155, side switch arm 156, firstposition, conductor 204, through the windin of the primary magnet 205 ofthe final se ector switch, conductor 206, middle right-hand armature andback contact of relay 145 to grounded battery. Relay 154 is operated inthis circuit, but being slow-to-release remains ener ized throughouteach series of impulses. fielay 150 being slow-to-release also remainsenergized during the sending of impulses. Primary magnet 205, inresponse to these impulses, steps the brushes 207, 208 and 209 to thegrou of terminals in which the line desired by t e calling subscriberappears. At the end of this series of im ulses, rela 137 holds itsarmature attracte for a su cient time to allow relay 154 to bedeenergized. When relay 154 was energized it completed a circuit fromround, outer armature and back contact 0 the final selector releasemagnet 213, conductor 214, front contact and right-hand armature ofrelay 154, conductor 166, back contact and armature of relay 167 throughthe windin of selector escape ma net 168, to grounde battery. Magnet 168is energized in this circuit, and when this circuit was broken by thedeener ization of relay 154, magnet 168 became eenergized to pass theselector side switch arms into position 2.

Establishment of a connection to another private branch exchangestation.

previously traced through relay 154, conductor 155, side switch arm 156,second position, conductor 215, through the winding of the selectorsecondary magnet 216, to grounded battery. Secondary magnet 216 isoperated by these impulses 'to'step brushes 207, 208 and 209, intoengagement with the terminals 210, 211, 212 of the wanted line. Belay154 and escape magnet 168 are also operated in the impulse circuit andat the conclusion of the im ulses, relay 154 in being deenergized brea sthe circuit of escape magnet 168 to allowit to become deenergizcd.Magnet 168 in being deenergized passes the selector side switch'intoposmon 3. If the called line is busy, ground potential will be found onits test terminal 212. This ground being applied through brush 209,conductor 169, side switch arm 170, third position, innermost left-handarmature and back contact of relay 171 through the right-hand winding ofrelay 172, and side switch arm 163, third-position, will shunt theright-hand winding of relay 162 which'is also connected over conductor161 and the circuit previously traced to ground at the front contact andright-hand armature of relay 150.

Relay 162 will therefore become deenergized and close a circuit fromgrounded battery through the winding of relay 145, conductor 173, backcontact and armature of relay 162, conductor 174, outermost lefthandarmature and back contact of relay 171, conductor 175, selector primary0E- normal spring 17 6 to ground. Relay 145 in being energized completesa circuit for release magnet 213 from grounded battery,

winding of release magnet 213, conductors 177 and 178, innermostright-hand armature and front contact relay 145, to ground throughprimary off-normal spring 176. The

release magnet 213 is energized in this circuit and locks up over acircuit from grounded battery through its winding, front contact andinner armature and conductor 175 to ground at ofi normal spring 176. Theenergization of the release magnet restores the selector switch tonormal.

When relay 145 was energized it completed a locking circuit for itselffrom grounded battery through its winding, lefthand armature and contactspring 160, conductor 159, left-hand armature and back contact of magnet158, conductor 157, front contact and right-hand armature of relay 150,to ground. When the selector switch reaches normal, the subscriber at Awill receive a busy tone which is transmitted over the followingcircuit: ground, secondary winding 179 of tone source B. T. outermostright-hand armature and front contact of relay 145, side switch arm 146,first position, conductor 147, condensers 148 and 149 and thence overthe circuit previously traced for the dial tone over conductor 143 toground through the right-hand winding of relay 137. The subscriberhearing this tone trfplages his reeiverh on its svfvitch-hool ere ym rruing t ecircuit o relay 13 Relay 137 in becoming deenergized opens thecircuit of relay 150. After a short interyal this relay is deenergizedand opens at its right-hand armature the circuits for relays 120, 107and 145. Relay 120 in being dcenergized 4 completes a circuit fromgrounded battery through the winding of finder release magnet 158, outerleft-hand armature and back contact of relay 120, conductor 180, backcontact and armature of relay 137, spring 151 to ground. The releasemagnet 158 is energized in this circuit and locks up from groundedbattery through its winding, front contact and right-hand armature andspring 151 to ground. The release magnet 158 restores the line finderswitch 100 to normal, at which time spring 151 opens to break thelocking circuit of magnet 158 and the systern is ready for the nextcall.

f, however, substation B is found idle when the selector side switchpasses to position 3, a circuit is completed from grounded batterythrough the winding of cut-ofi relay 216, terminal 212, brush 209,conductor 169, side switch arm 170, third position, innermost left-handarmature and back contact of relay 171, through the right-hand windingof relay 172, side switch arm 163, third position, right-hand winding ofrelay 162, conductor 161, contact spring 160, conductor 159, left-handarmature and back contact of relay 158, conductor 157, front contact andright-hand armature of relay 150 to ground. Relays 172 and 216 areenergized in this circuit and relay 162 is maintained energized. Relay172, in being energized, connects ground over its front contact andright-hand armature, contact and innermost left-hand armature of relay171 and side switch arm 170, third position, over brush 209 to testterminal 212 to render the called line immediately busy. This groundalso shunts the right-hand windings of re.- lays 172 and 162 but theyare not deenergized since a substitute circuit is completed immediatelyfrom grounded battery through the left-hand winding of relay 162, sideswitch arm 181, third position, left-hand winding, left-hand armatureand front contact of relay 172, conductor 155, side switch arm 156,third position, to ground. The-es cape magnet 168 is energized over acircuit from grounded battery, through winding of magnet 168, armatureand back contact of relay 167, conductor 166, over the circuit justtraced to ground at side switch arm 156, third position. Magnet 168 inbeing energized completes a circuit to apply ringing current to thecalled line which may be traced from a source of ringing current 11through the winding of ringing cut-ofi relay 167, side switch arm 182,thir tion, ont contact and inner left-hand armat re of magnet 168,conductor 147, s1de switch arm 183 third position, conductor 184, sideswitch arm 185, third position, conductor 186, brush 208, terminal 211,through the bell (not shown) substation B, term nal 210, brush 207,conductor 187, s1de switch arm 188, third position, conductor 189, s1deswitch arm 190, third position, conductor 191, outer left-hand armatureand front contact of magnet 168, to ground. Belay 167 is marginal andwill not be energlzed in the circuit just traced until the calledsubscriber answers. When the called subscrlber answers he lowers theresistance of the ringin circuit by shunting the bell with his swltchook, and relay 167 is energized. In belng energized, relay 167 opensthe circuit previously traced for escape magnet 168, and

escape magnet 168 is deenergized to pass the selector side switch intoposition 4.

Substations A and B are now connected over conductors 140 and 141, sideswitch arm 142, third position, condenser 193, Side switch arm 190fourth position, conductor 189, side switch arm 188 third position,conductor 187, brush 207, terminal 210, substation B, terminal 211,brush 208, conductor 186, side switch arm 185 third position, conductor184, side switch arm 183, fourth position, condenser 149, side switcharm 122 third position, conductors 138 and 139, brush 118, terminal 133,conductor 115, through substation A, terminal 134 and brush 119 toconductor 140. Talking current is supplied to the calling line throughrelay 137, and to the called line from grounded battery, through theleft-hand winding of impedance coil 192, side switch arm 183 fourthposit-ion and side switch arm 185 third position, ring conductor 186,thence through substation B, tip conductor 187 side switch arm 188 thirdosition and side switch arm 190 fourth position, through the right-handwinding of impedance coil 192, to ground. Relay 162 is held energizedthroughout the conversation over a circuit from grounded battery,left-hand winding relay 162, side switch arm 163 fourth position,right-hand winding relay 162, conductor 161 and over the circuitpreviously traced to ground at the right-hand armature of "relay 150.Ground is also applied to the sleeve terminal of the called line throughside switch arm 170 fourth position, conductor 169, brush 209, andterminal 212 to hold cut-ofi' relay 216 energized, and to furnish a busytest at the multiples of line B in other switches. At the conclusion ofthe conversation, the calling subscriber in placing his receiver on itsswitc'hhook, opens the circuit of relay 137 which becomes deenergized toopen the circuit of relay 150. Relay 150, in being deener ized opens thecircuit of relays 120 and 16%; finder release magnet 158, and seearnerlector release magnet 213 are energized to release the finder andselector switches in the manner described when line B was foun to bebusy.

Establishment of a connection to a central ofice trumk.

If the subscriber at station A desires a central ofiice connection, 11on hearing the dial tone when the finder si e switch reaches position 3,he operates his sender to set selector switch 200 on a level 400 in thefinal selector bank which leads to central ofiice trunks. The operationof the finder switch and the selector switch in its prima movement isthe same as when a ticu ar station B was desired. At the end of thefirst series of impulses however, auxiliary brush 201 will be inengagement with commutator segment 202 which is individual to thecentral oflice level. Upon the deenergization of relay 154 at theconclusion of the first set of impulses, magnet 168 is deenergized topass the side switch into position 2, and ground is applied throughspring 176, conductor 175, lefthand armature and back contact of relay154, conductor 194, brush 201, commutator segment 202, conductor 195, tothe armature of relay 196. If the substation A is restricted to branchexchange calls, its cut-off relay 114 will be connected to terminal 116through the left-hand winding only, and relay 196 will be energized overa circuit from grounded battery, left-hand winding relay 114, terminal116, brush 117, side switch arms 111 and 110, third position through thewinding of relay 196 to ground.

The ground of sprlng 176, appearing at the armature of relay 196 willtherefore be extended over conductor 177 through the winding of releasemagnet 213 to grounded battery. Magnet 213 will be energized and lockedup in the same manner as before and release of the selector switch willtake place precisely as though selector 200 had been set on theterminals of a busy substation within the branch exchange. The callingsubscriber will receive a busy tone as before and will hang up torelease line finder 100 as before.

If, however, substation A is a non-restricted station, its cut-off relay114, will be connected to terminal 116 through both windings in series,and relay 196 being marginal will not be energized. in the circuitpreviously traced. The ground on the armature of relay 196 willtherefore be extended over the back contact of relay 196, side switcharm 197,- second position, through the winding of relay 171 to groundedbattery. Relay 171 is energized, and locks up over a circuit fromgrounded battery through its winding, right-hand armature and front cona conductor 198 and conparductori161 over the circuit previously tracedfor relay 162 to ground, at the right-hand armature of relay 150. Acircuit is thereupon completed from grounded battery through the windingof magnet 168, armature and back contact of relay 167, middle left-handarmature and front cont-act of relay 171, conductor 199, secondaryofi-normal spring 10, which is. closed until the secondary movement ofthe selector switch begins, spring 176 to ground. Escape magnet 168 isenergized in this circuit and held up over a circuit through side switcharm 170, second position, conductor 169, and brush 209 to ground on busyterminals 219 of central ofiice trunks after the secondary movement ofthe selector switch opens contact spring 10. A circuit is also completedfrom grounded battery through the winding of secondary magnet216,conductor 215, side switch arm 156, second position,conductor 155,conductor 220, back contact and armature of magnet 216, conductor 221,side switch arm 146, second position, inner armature and front contactof magnet 168, side switch arm 182, second position, innermost left-handarmature and front contact of relay 171, conductor 198 and thence inparallel with the locking circuit of relay 171 to ground at theright-hand armature of relay Stepping magnet 216, makes and breaks thiscircuit at its armature and back contact, and steps the brushes 207,208, 209, over the terminals of central oflice trunks until an idletrunk, indicated by battery potential at test contact 219, is found. Atthis time, escape magnet 168 is shunted by the battery potential appliedthrough brush 209, side switch arm 170, second position, middleleft-hand armature and front contact of relay 171, and back contact andarmature of relay 167. Escape magnet 168 is deenergized to pass theselector side switch into position 3, and to open at its inner lefthandarmature the circuit of the secondary magnet 216.

In position 3 of the selector side switch, a circuit is completed forfinder escape magnet 129 from grounded battery through the winding ofmagnet 112, winding of magnet 129, conductor 128. side switch arms 127and 197, third position, right-hand armature and front contact of relay171, and thence in parallel with the locking circuit of relay [71 overconductors 198 and 161 to ground, at the right-hand armature of relay150.-- Escape magnet 129 is energized in this circuit and advances thefinder side switch to position 4.

In position 4 of the finder side switch the circuit of stepping relay137 is interrupted at side switch arms 123 and 142, fourth position, andthis relay is deenergized to open the circuit of relay 150. Relay 150,however, is slow-to-release and is not deenergized at once, butmaintains the circuits of relays 171, 120 and 107, and completes acircuit in parallel with said circuits from round at the right-handarmature of reay 150 over conductor 157 the circuit previously traced toconductor 198, front con tact and innermost left-hand armature of relay171, side switch arm 170, third position conductor 169, brush 209,terminal 219, conductor 222, through the winding of relay 301 togrounded battery. Relay 301 is energized in this circuit and completes acircuit to energize relay 303 which may be traced as follows: ground,right-hand armature and back contact of relay 302, left-hand armatureand front contact of relay 301, winding of relay 303 to groundedbattery. Relay 303 in being energized completes a circuit from ground,front contact and outer right-hand armature of relay 303, through thewinding of relay 304 to grounded battery. Relay 304 is energized andconnects the trunk conductors 223and 224 to the armatures of relay 305.In being energized, relay 303 also completes a circuit from ground,front contact and left-hand armature of relay 303, conductors 306 and307, outer right-hand armature and back contact of relay 308, throughthe winding of. relay 305 to grounded battery. Relay 305 is energized tocomplete a circuit from grounded battery through the right-hand windingof relay 309, front contact and inner armature of relay 305, frontcontact and outer armature of relay 304, ring conductor 223, terminal218, brush 208, conductor 186, side switch arm 185, fourth position,conductor 139 through the finder brushes and apparatus at substation A,back over tip conductor 140, side switch arm 188, fourth position,conductor 187, brush 207, terminal 217, conductor 224, inner armatureand front contact of relay 304, outer armature and front contact ofrelay 305, through the left-hand winding of relay 309 to ground. Relay309 is energized in this circuit and closes a circuit from groundedbattery through the winding of slow-to-release relay 302, front contactand right-hand armature of relay 309 to ground. Relay 302 in attractingits armatures applies ground through its lefthand armature and frontcontact to conductor 222 to take the place of the ground formerlyapplied through the right-hand armature of relay 150 to hold up relays301, 171, 107 and 120.

When relay 309 was energized it also completed a circuit, from ground,left-hand armature and front contact ofrelay 309, conductors 310 and317, through the winding of relay 311, conductor 312, armature and backcontact of relay 313 through the winding of relay 314 to groundedbattery. Relay 314 is energized in this-circuitbut relay 311 is marginaland will not be energized in series with relay 314 which is high wound.Line relay 314 in being energized completes a circuit for call lamp L atthe central ofiice operators position. The operator seein lamp L lightedinserts the plug 315 of 181 cord circuit in jack 316 of the linecalling. A circuit is thereb completed from .grounded battery, le t-handlower winding of repeating coil 318, winding of supervisory rela 319,ring 320, contact Spring 321, con uctor 312, through the winding ofrelay 311, conductors 317 and 310, front contact andleft-hand armatureof relay 309 to ground. The resistance of supervisory relay 319.isrelatively low, so that both marginal relay 311 and relay 319 areenergized in this circuit. Relay 319 in being ener 'ized extinguishesthe calling supervlsory amp (not shown). When the operator inserted plug315 into jack 316, a circuit was also completed from grounded battery(not shown), through the sleeve of plug 315 and jack 316 and the windingof cut-ofi' relay 313 to ground. Cut-oflt' rela 313 was energized toextinguish the cal lamp L. Relay 311 in being energized completes acircuit from ground, armature and front contact of relay 311 through thewinding of relay 308 to grounded battery. Relay 308 is energized and atits outer righthand armature breaks the circuit of relay 305. At itsleft-hand armature it closes a low resistance shunt circuit to provide apath for voice current around relay 311 through conductor 322,resistance 323, front contact and left armature, of relay 308, back tothe ring conductor 317. Resistance 323, however, is not small enough to'cause relay 311 to be deenergized. Relay 305 in being deenergized.connects the talking conductors 224 and 223 through to the contactsprings of relay 324 and interrupts the circuit of relay 309. Relay 309in,being deenergized breaks the circuit of relay 302,

but this relay is slow-to-release and stays' up until a substitutecircuit is completed as will appear hereinafter.-

Relay 308, in attracting its inner right-hand armature completed acircuit from ground, inner right-hand armature of relay 308,

through the winding of relay 324 to grounded battery. Relay 324 islocked up over a circuit from grounded battery through its winding,front contact and right-hand armature over conductor 306, left-handarmature and front contact of relay 303 to ground. A circuit is alsocompleted from grounded battery through the winding of slow-to-releaserelay 325, front contact and outer right-hand armature'of relay 308,conductors 307 and 306 to ground at the front contact andlefthandarmature of relay 303.- Relay 325 in attracting its armaturecompletes the substitute circuit for holding up relay 302 from groundedbattery through thetw'inding of relay 302, front contact and armature ofrelay 325 to ground.

A talking circuit is now completed from substation A over the conductorsshown in heavy black to the central ofiice. The central ofiice operator,by depressing a listening key (not s own) may inquire the number desiredby the callin subscriber and may thereupon complete t e connection tothe wanted subscriber in any well known man ner.

The release of the connection will occur upon the deenergization ofrelay 311. At the close of the conversation the calling party inreplacing his receiver on its hook breaks the circuit throughsupervisory relays, 311 and 319. Relay 319 in being deenergized lightsthe calling supervlsory lamp (not shown) before the operator who removesplug 315 from jack 316. Relay 311 in being deenergized opens the circuitof relay 308 which retracts its armatures. At its outer ri ht-handarmature relay 308 breaks the circuit of relay 325 which retracts itsarmature to break the circuit of relay 302. Relay 302 in beingdeenergized, removes ground from conductor 222 thereby opening thecircuits of relays 303, 171, 107 and 120 which relays become inert.Relay 303 in retracting its armatures opens the circuits which had heldup relays 304 and 324, and the trunk circuit is now in normal condition.Relay 171 in being deenergized completes a circuit for release controlrelay 145 which may be traced from grounded battery, relay 145,conductor 173, back contact and armature of relay 162, conductor 174,outer-most left hand armature and back contact of relay 171, conductor175, through off-normal spring 176 to ground. Relay 145 attracts itsarmatures and completes the previously traced circuit for selectorrelease magnet 213. This magnet causes release of the selector switch inthe same way as described for a call between station A and station B.Relay 120 in being deenergized com pletes the previously traced circuitfor finder release magnet 158 which is energized to release the finderswitch in the manner previously described and the system is now readyfor another call.

Establishment of a connection to a receiving subsem'be'rs station.

pulses to set the selector switch on level arm 197, second position,through the wind-- ing of relay 171, to grounded battery. Relay 171 isenergized and locks up through its right-hand armature and front contact7 and conductor 1.98 to ground at the righthand armature of relay 150over the circuit previously traced. A circuit is then completed fromground through off-normal contact 176, secondary off-normal contact 10closed until'the initiation of secondary movement, conductor 199, middleleft-hand armature and front contact of relay 171, back contact andleft-handarmature of relay 167 through the escape magnet 168 to groundedbattery. Magnet 168 is energized in this circuit and after the switchhas taken its first secondary step and the off-normal con tact 10 isopened, is maintained energized in a circuit from battery, winding ofmagnet 168, armature and back contact of relay 167, front contact andmiddle left-hand armature of relay 171, arm 170, second position andbrush 209 to ground on busy test terminals 229 of receiving subscriber-strunk lines. A circuit is also completed from grounded battery throughthe winding of secondary magnet 216, conductor 215, arm 156, secondposition, conductors 155 and 220, back contact and armature of magnet216, conductor 221, arm 146, second position, inner armature and, frontcontact of magnet 168, arm 182, second position, innermost left-- handarmature and front contact of relay 171, and thence in parallel with thelocking circuit of said relay to ground at the righthand armature ofrelay 150. The secondary magnet 216 makes and breaks this circuit at itsleft-hand armature and passes the se lector brushes over terminals 227,228 and 229, until an idle set of terminals is reached. The idlecondition of these terminals being denoted by absence of ground onsleeve terminal 229, the locking circuit of escape magnet 168 is brokenand magnet 168 is deenergized to pass the selector side switch intoposition 3. In opening its inner arma ture, magnet 168 permanently opensthe circuit of secondary magnet 216 to stop the brushes 207, 208 and 209in engagement with the idle set of terminals. 1

In position 3, of the selector side switch a circuit is completed forfinder escape magnet 129 from grounded battery through the winding ofmagnet 112, magnet 129, conductor 128, arms 127 and 197, third positionright-hand armature and front contact of relay 171, and thence inparallel with the locking circuit of relay 171 to ground at theright-hand armature of relay 150. Escape magnet 129 is energized in thiscircuit to advance the finder side switch to position 4. In position 4of the finder side switch the circuit of stepping relay 137 isinterrupted at side switch arms 123 and 142, fourth position, and thisrelay 137 is deenergized to open the circuit of relay 150. Relay 150,however, is slow-to-lease and is not deenergized at once, but maintainsthe circuits of relays 171, 120 and 107 until a substitute ground isprovided from the selected trunk circuit. With the finder side switch inposition 4, and the selector side switch in position 3, a circuit iscompleted from grounded battery through the righthand winding of linerelay 230, back contact and innermost left-hand armature of relay 231,terminal 228, brush 208, conductor 186, arm 185, fourth position,conductor 139, brush 118, terminal 133, through the apparatus at stationA, terminal 134, brush 119, conductor 140,-arm 188, fourth position,conductor 187, brush 207, terminal 227, middle left-hand armature andback contact of relay 231 through the left-hand winding of relay 230 toground. Relay 230 is energized and completes an energizing circuit forslow-to-release relay 232. Relay 232 in attracting its armature appliesground to terminal 229 to replace ground formerly applied at theright-hand armature of relay 150 for providing a busy test, and holdingup relays 171, 107, and 120. A circuit is also completed from ground,armature and front contact of relay 232, conductors 233 and 234, sideswitch arm 235, first position, right-hand armature and back contact ofrelay 236, back contact, armature and winding of motor magnet 237 togrounded battery. Magnet 237 makes and breaks this circuit at itsleft-hand armature and steps brushes 238, 239 and 240 of the huntingswitch 25 over terminals 241, 242 and 243 of receiving subscriberslines. Busy lines are denoted by ground on their test terminals 243which shunts the right-hand winding of test relay 236 over brush 240.When an idle line is reached, a circuit is completed from groundedbattery through both wind ings of cut-off relay 244, terminal 243, brush240, right-hand winding of test relay 236, arm 235, first position,conductors 234 and 233 to ground at the front contact and armature ofrelay 232. Relay 236in being energized interrupts the circuit of magnet237 to stop the switch on the selected set of terminals, and at itsleft-hand armature completes a circuit from grounded battery through thewinding of relay 245, left-hand winding, front contact and armature ofrelay 236, thence over the circuit previously traced to ground at thearmature of relay 232. This circuit energizes relay 245 and holds uprelay 236 after its right-hand winding has been shunted by theattraction of its ri 'ht-hand armature to provide a busy ground atterminal 243. Relay 245 in attracting its right-hand armatures completesa circuit to ring the call bell if the receiving subscriber is equip edwith the type of apparatus shown at or to energize its re ay 326 if thestation has the equipment shown at F, which circuit may be traced from asource of ringing current through the right-hand winding of relay 246,back contact and inner right-hand armature of said relay, front contactand inner right-hand armature of relay 245, brush 239, terminal 242through the call hell or relay, according to the equipment at thereceiving station, terminal 241 brush 238, outer right-hand armature andfront contact of relay 245, outer right-hand armature and back contactof relay 246 to ground. Relay 246 is marginal-and will not be ener gizedin this circuit until the resistance is lowered when the calledsubscriber answers in the case of station E, or throws his answering key327 in the case of station F.

At this time relay 246 attracts its armatures to interrupt the callingcurrent and com pletes at its left-hand armature a holding circuit foritself which may be traced from grounded battery, left-hand winding ofrelay 246, left-hand armature and front contact of said relay, frontcontact and lefthand armature of relay 245 to ground. In attracting itsright-hand armatures, relay 246, also completes a connection between thecalling substation and the (receiving' substation, talking current beingsupplied through both windings of relay 230. Supervisory relay 247 isenergized in the talking circuit. 7

Transfer 0 a call from a receiving subscribers statzon to a regularprivate branch exchange station.

The calling subscriber may now obtain any information he desires fromthe receiving subscriber. In case it is desired to extend the connectionto a substation within the branch-exchange such as that shown at C, thereceiving subscriber operates his calling'device to lnterrupt thecircuit through supervisory relay 247. When relay 247 was firstenergized it completed a circuit from grounded battery through thewinding of slow-to-release relay 248, conductor 249, front contact andarmature of relay 247 to ground. When relay 247 becomes deenergized inresponse to the first impulse caused by the operation of the receivingsubscrlbers sender, a circuit is completed from. ground,

armature and back contact of relay 247, normal contact 250 of relay 251,inner righthand armature and front contact of relay 248, through thewinding of slow-to-releasa relay 252, side switch arms 253 and 254,first position, front contact and inner armature of relay 255, throughthe winding of primary magnet 256 to rounded battery. Relay 255 wasenergized when relay 232 first attracted its armature, over a circuitfrom grounded battery, right-hand winding of relay 255, arm 259, firstposition, lefthand winding of relay 255, conductor 257, back contact andarmature of release magnet 258, conductor 233 to ground at the frontcontact and armature of relay 232. Magnet 256 steps the brushes 260, 261and 262 of companion final switch 20, over the termi nals in its bank.In case the called substation is not in the first group of terminals,the receiving subscriber in operating his calling device will send morethan one primary impulse. In response to the first impulse,slow-to-release relay 252 is energized and remains operated throughouteach series of impulses. Relay 252 completes at its lefthand armature anenergizing circuit for relay 251 from ground, left-hand armature andfront contact of relay 252, through relay 251 to grounded'battery.A'circuit is also completed from grounded battery through the winding ofcompanion final escape magnet 263, armature and back contact of relay264, conductor 265- to ground at the front contact and left-handarmature of relay .252. When relay 251 was energized it com leted acircuit for relay 266 from groun ed battery, right-hand windin relay266, front contact and inner leftand armature of relay 251, thence overthe talkingflconductors through the a paratus atY-I su s tation E, andback throng left-hand armature and front contactof relay 251 andleft-hand winding of relay 266 to ground. Relay 266 in attracti itsarmature provides a substitute circuit to hold up relay 248 after relay247 has retracted its armature during the first'impulse. In response tosucceeding interruptions caused bv t e operation of the sender atsubstation I l,

relay 266 vibrates its armature. Each time the outer that the armatureof relay 266 is retracted,

. to the terminals of the desired line.

relay 252 to become deenergized; Relay 252 in being deenergized opensthe circuits previously traced for relay 251 and for the escape magnet263. Magnet 263 in being deenergized steps the"-- companion final sideswitch into position 2. Relay 251 in being deenergized again completesthe circuit from relay 230 through the substation E which operates relay247.

The receiving subscriber now sends a series of lmpulses to set theswitch 20 on the terminals of the desired line. In response to the firstof these impulses, relay 247 is deenergized to complete a circuit fromgrounded battery through the winding: of the secondary magnet 267, arms254, and 253,.second osition, through the winding of relay 252, rontcontact and inner righthand armature of relay 248,- normal contact 250ofrelay 251 to ground at the back contact and armature of relay 247.Relay 252 is energized in this circuit and operates relay 251 and theescape magnet 263 in the same manner as during the primary impulses. Thesecondary magnet 267 steps the brushes 260, 261 -and'262 of switch 20one step in their secondary movement. In case more than one impulse issent, relay 266 is againincluded in thecircuit with the sender atsubstation E and vibrates its armature to complete the circuit for secondary magnet 267 from ground, armature and back contact of relay 266,righthand armature of relay 251 and contact lever of normal contact ofrelay 251, inner right-hand armature and front contact of relay 248 andthence over the path traced for the first impulse through the winding ofsecondary magnet 267 to grounded battery. Magnet 267 in response tothese impulses steps the brushes of the switch 120 t the conclusion ofthis series of impulses, relay 266 remains energized to break thecircuit of relay 252, and after a short interval this relay retracts itsarmatures to open the circuits of relay 251 and escape magnet 263.Magnet 263 in being deener-.

' gized, passes the "side switch into position 3. Relay 251, inretracting its left-hand armatures again completes the circuit betweenstation A and station E to energize relay 247. Relay 248 being slow torelease remains energized as long as the receiving subscriber holds hisconnection, since it is energized over a circuit from grounded batterythrough its winding to ground at either the armature and front contactof relay 247, or of relay 266 since one of these relays is energized atall times until station E is disconnected from the line. Relay 248 atits leftha.nd armature provides a substitute circuit for holding uprelay232 in case the calling subscriber should, by abandoning the call,open the circuit of line relay 230. Release is therefore under thecontrol of the receiving. subscriber while line is busy, ground on itstest terminal.

will be connected through brush 262 and arm 272, third position, to theleft-hand winding of relay 271 to shunt this relay which is alsoconnected to ground through the outer left-hand armature and backcontact of relay 273, arm 259, third position, left-hand winding ofrelay 255, conductor 257, back contact and armature of magnet 258 andconductor 233 to the front contact and ground at armature of relay 232.As no circuit is now completed for relay 255, it retracts its armaturesto complete a cir cuit for magnet 258 which may be traced from groundedbattery through the winding of magnet 258, outer armature and backcontact of relay 255 through rimary ofiirormal spring 274 to ground. l.elease magnet 258 is energized in this circuit and restores thecompanion final brushes and side switch arms to normal, at whichtime-ofinormal spring. 274'opens to break the Circuit through 'magnet258. In attracting its armature, magnet 258 completes a circuit ,fromgrounded battery through the winding of relay 27 5, front contact andarmature of magnet 258 and conductor 233, to ground at the front contactand armature of relay 232. Relay 275 is energized in this circuit andlocks up over a circuit from grounded battery through its winding frontcontact and right-hand armature and conductor 276 to ground, at thefront contact and armature of irelay 247. In attracting its left-handarmature, relay 275 completes a circuit from ground, through thesecondary. winding of busy tone source 287, front contact and left-handarmature of relay 275, inner left-hand armatureand back contact? ofrelay 277 throughthe condenser 278 and tip conductor 279 throu h thereceiving subscribers substation thence back over the ring conductorthrough the innermost armature and back contact of relay 231 to theright-hand winding of relay 230 and grounded battery.

The receiving subscriber hearing this busy tone informs the callingsubscriber that the called line'is busy and may then, by operating hissender, reset the companion final switch 20 in accordance with thedesire of the calling subscriber, or he may release the entireconnection by replacing his receiver on its hook. The operation ofresctting the companion final switch is the same as when this switch wasfirst set and need not, therefore, be described. If the subscriberdoes-not desire any further COTI nection'; the receiving subscriber inreplacing his receiver on its book interrupts the circuit for relay 247,and relay 266 being inert at this time, relay 248 is deenergized tobreak at its lcft-hand armature the sub stitute circuit for relay 232.When thecalling subscriber hangs, up his receiver he breaks at hisswitch-hook the circuit for relay 230, In becoming deenergized, relay230 interrupts at its armature the circuit for relay 232 whichthereuponis deenei' gized. Relay 232 in becoming deenergized removes the holdingground from terminal 229 thercby interrupting the circuits of relays 171and 120. Relays 171 and 120' are deenergized to cause the restoration ofthe selector and finder switches in the manner previously described whena central ofiice call was made from station A. Relay 232 in beingdeencrgized also completes a circuit from ground, armature and back contact of relay 232, outermost left-hand armature and back contact "ofrelay 231 through spring 280 closed when hunting switch 25 isoff-normal, through the winding of magnet 281 to grounded battery.

Magnet 281 is energized to restore hunting. switch 25 to normal positionat whlch time spring 280 opens to render magnet 281 inert. The system isnow ready for the next call. v

If the line C, when tested, is found to be idle, no ground will appearon its sleeve terminal 27 0, and a circuit will be completed fromgrounded battery through the winding of cut-off relay 282, terminal 270,brush 262, arm 272, third position, through the left-hand winding ofrelay 271, back contact and outer left-hand armature of relay 273, arm259, third position, through. the left-hand winding of relay 255, backcon;

tactand armature of magnet 258 over con-- ductor 233 to ground at thefront contact and armature of relay 232. Cut-off relay 282 and testrelay 271 are energized in this "circuit, and release control relay. 255is maintained energized. Relay 271 in attracting its left-handarmatureconnects a dead ground to terminal 270 to provide a busy test and toshunt the left-hand winding of relay 271. Relay 271 is not deenergizedhowever, since a substitute-circuit is completed from grounded battery.to the righthand Winding of relay 255, arm 283, third position,right-hand winding, front contact and armature, of relay 271, conductor257 to ground at the armature of relay 232 over the circuit previouslytraced. Relays ing its armatures closes a circuit to ring the call bellat substation C which may be traced from a source of ring currentthrough the winding of ringing trip relay 264, inner armature and frontcontact of magnet 263, arm 284, third ,position, brush 261 terminal 269,through the apparatus at station (J, terminal 268, brush 260, arm 285,third position, outer armature and front contact of magnet 263 and arm286, third position, to ground. Relay 264 is marginal and will not beenergized in this circuit until the subscriber at C lowers theresistance of ,the ringing circuit by removing his receiver from itshook. Relay 264 thereupon is energized and breaks at its armature thecircuit of escape magnet 263. Escape-magnet 263 in becoming deenergizedpasses the companion final side switch into fourth position; Stations Aand C are now connected through companion final brushes 260, and 261,arms 285 and 284, fourth position, selector terminals 227 and 228,selector brushes 207 and 208, arms 188 and 185, fourth position, and theconductors shown in heavy black. In fourth position, release controlrelay 255 is held energized over a circuit from 'grounded batterythrough the right-hand winding of relay 255, arm 259, fourth position,left-hand winding of relay 205, conductor 257, back contact and armatureof magnet 258, and conductor 233, to ground at the armature of relay232. Ground is connected through the right-hand armature'and backcontact of relay 277, arm 272, fourth position, and brush 262 toterminal 270, to provide busy potential and to hold cut-off relay 282'en-- ergized, Talking current is supplied through both windings of relay230. Side switch arm 235 in passing to fourth position interrupts theholdingcircuit for relays 245 .and 236. Relay 245 when deenergizedinterrupts at its left-hand armature the circuit for relay 246, and atits right-hand armatures the circuit for relay 247. Relay 247 in beingdeenergized breaks the circuit to be busy and the receiving station E isready for the next call.

When the subscribers at A and C complete their conversation, and hang uptheir receivers, they interrupt at their switch-hooks the circuit ofrelay 230. Relay 230 in being deenergized opens the circuit of relay 232which retracts its armature. Ground being removed from conductor 233 andterminal 229, release control relay 255 retracts its armature tocomplete a circuit formagnet 258. Relays 171 and 120 also retract theirarmatures, and release of switches 100, 200 and 20 takes place in themanner described when substation C- was found to be busy.

lz'stablz'slzment of a connection from a restricted service station to acentral .ofice trunk.

pose of-getting information. The hunting switch 25 picks an idlereceiving subscriber in the manner previouslydescribed and substation Ais then connected to a receiving station such as E. The callingsubscriber informs the receiving subscriber of his desire for a centralofiice connection, and the receiving subscriber may, at his discretion,extend the call to the central, ofiice. To do this, the receivingsubscriber operates his sender to set the companion final brushes 260,261, and 262 in their primary movement on a level 400 in which appearterminals of central oflice trunks. The operation of the final switch inits primary movement is accomplished in the manner previously describedwhen a call was being extended to a substation C within the exchange,except that at the end of the primary movement auxiliary brush 288 willrest on commutator segment 289 individual to the central office level.WVhen relay 252 is deenergized at theend of the primary impulses, acircuit is completed from grounded battery through the winding of relay273, conductors 290, 291 and 292, commutator segment 289, brush 288,conductor 293, back contact and righthand armature of relay 252,conductor 257,

back contact and armature of magnet 258,

hand armature and front contact of relay 27 3, conductor 257, and thenceover the circult just traced to ground at the right-hand armature ofrelay 232. Release control relay 255 is held up in first and secondosit1ons from grounded battery rightand winding of relay 255, arm 259,iirst position, left-hand winding of relay 255, conductor 25? to groundat the armature of relay 232.

When relay 252 became deenergized it also interrupted at its left-handarmature and inner front contact, the circuit for escape magnet 263.Magnet 263 in being deenergized passes the side switch into secondositlon. In second position of the side swltch, escape magnet 263 isagain energized over a circuit from grounded battery through the windingof magnet 263,'armature and back contact of relay 264, conductor 265,front contact and outer right-hand armature of relay 273, conductor 294,arm 272, second position, and brush 262 to onnd on terminals 219 of-busycentral 0 cc trunks. Magnet 263-in attracting its outer armaturecompletes a circuit from -grounded battery through the winding ofsecondary magnet 267, arms 254 and 253, second position, armature andback contact of magnet 267 inner right-hand armature and front contactof relay 273, outer armature and front contact of magnet 263, arm 286,second position, conductors 257 and 233 to ground at the armature ofrelay 232. Secondary magnet 267 makes and breaks this crcuit at itsarmature and back contact, and steps the brushes 260, 261 and 262 overthe terminalsof central ofiice trunks. When an idle set of terminals isfound, absence of ground potential on test terminal 219 opens thecircuit which has been holding up magnet 263, to allow this magnet to bedeenergized. Magnet 263 in being deenergized passes the side switch intothird position and at its outer armature breaks the circuit of secondarymagnet 267 to stop the brushes 260, 261 and 262 in engagement withterminals 217, 218 and 219 of the selected trunk line.

Relay 277 was energized in parallel with relay 273 and had a holdingcircuit provided from grounded battery through the winding of relay 277,conductors 291 and 290, inner left-hand armature and front contact ofrelay 27 3 and thence in parallel with the locking circuit of relay 273to ground at the armature of relay 232. When the side switch reachesthird position, ground', is therefore applied to terminal 219, throughthe armature of relay 232, conductor 233, back contact and right-handarmature of relay 231, contact springs 296 of relay 277, arm 272, thirdposition, and brush 262 to energize relay 301 and to provide busy potureand back contact of relay 264, conductors 265 and 297, arms 253 and 254,third position, front contact and outer left-hand armature of relay 277to ground. A circuit is thereupon completed from' a source of ringingcurrent, through the wind1ng of relay 264, front contact and innerarmature of magnet 263, arm 298, third position, back contact andleft-hand armature of relay 275, inner left-hand armature and frontcontact of relay 277, resistance 299, conductor 22, outer armature andfront contact of magnet 263, arm 286, third position to ground.Resistance 299 is low enough to allow relay 264 to be'energized in thiscircuit thereby interrupt'nl'gi-the circuit previously traced for theescape'ma net 263 which is deenergized to pass the si e switch intofourth position.

With the side switch in fourth position a circuit is completed toenergize relay 231 which may be traced from grounded battery, winding ofrelay 231, side switch arms 254, and 253, fourth, position, conductor290, inner left-hand armature and front contact of relay 273, and thencein parallel with the locking circuit of relay 273, to ground at thearmature of relay 232. Belay 231 in attracting its left-hand armaturesbreaks the circuit of relay'230 which in being deenergized opens thecircuit of relay 232. Relay 232 is slow-to-ielease and does nottherefore retract its armature until ground has been applied toconductor 233, from relay 302.in 'the'selected trunk circuit. Relay 301which it will be remembered was energized immediately upon the seizureof the trunk when the companion final side switch was in third pos tion.is held energized after the side switch passes to fourth position over acircuit from grounded battery through the winding of relay 301,conductor 222. terminal 219. brush 262. arm 272, fourth position,right-hand armature and contact springs 296 of relay 277, right-handarmature and front contact of relay 231, and thence in parallel with thecircuit just traced for relay 231 to ground at the armature of relay232.

The ener ization of relay 301, causes the same operation of the relaysin the trunk circuit as was described when the selector switch 200 wasset direct on terminals of such a trunk circuit, and need not bedescribed in detail here. When line relay 309 attracts its armatures toenergize relay 302, relay 302 at its left-hand armature applies groundto conductor 222 and thence through terminal 219, brush 262, arm 272,fourth position, right-hand armature and contact springs 296 of relay277, right-hand armature and front contact of relay 231, arms 254 and253, fourth position, conduct-or 290, inner left-hand armature and frontcontact of relay 273, conductor 257, back contact and armature of magnet258, conductor 233 to terminal 229. Relays 255, 273, 277 and 231 of thecompanion final switch are held energized in this circuit throughout theremainder of the connection. Relays 120, 107 and 171 are also held upover this circuit. \Vhcn the companion final side switch passed intofourth position, the receiving subscriber at station E was disconnectedand the switch 25 was restored in the same manner as was described whena call was completed between station A and station C.

The central ofiice operators call lamp L, Fig. 3, is lighted in the samemanner as was described when a direct central office call, without theintervention of a receiving subscriber,-was made and the operatorinserts her plug 315 in jack 316, thereby energizing relays 311 and 308in the manner previously described. and depresses her listening key (notshown). A talking circuit is now completed between the operators headset (not shown), and substation A, energy being supplied over a circuitfrom grounded battery lower left-hand winding of repeating coil 318,supervisory relay 319, ring 320, spring 321, conductors 312 and 322,resistance 323, front contact and left-hand armature of relay 308, innerleft-hand armature and front contact of relay 324, back contact andinner left-hand armature of relay 305, front contact and outerright-hand armature of relay 304, conductor 223, terminal 218, brush261, arm 284, fourth position, terminal 228, brush 208, conductor 186,arm 185 fourth position, conductor 139, brush 118, terminal 133, throughthe apparatus at substation A, terminal 134, brush 119, conductor 140,arm 188, fourth position,'conductor 187, brush 207, terminal 227, arm285, fourth position, brush 260, terminal 217, conductor 224, innerarmature and front contact of relay 304, outer armature and back contactof relay 305, front contact and outer left-hand armature of relay 324,conductor 328, spring 329, tip of plug 315, upper left-hand winding ofrepeating coil 318 to ground.

The operator inquires the number desired by the calling party andcompletes the connection in the usual manner. At the conclusion of theconversation when the calling subscriber replaces his receiver on itshook, he interrupts the circuit just traced which has been holdingsupervisory relays 311 and 319 energized. Relay 319 in being deenergizedlights its associated supervisory lamp (not shown) and the operatorremoves plug 315 from its jack. Relay 311 in being deenergized opens thecircuit of relay 308. Relay 308 in retracting its armatures closes thecircuit of relay 305 from grounded battery through the winding of relay305, back contact and outer right-hand armature of relay 308, conductors307 and 306, lefthand armature and front contact of relay 303 to ground.In case the calling subscriber at station A desires another centralofiice connection immediately, he does not leave his receiver on'itshook, but immediately removes. it, thereby completing acircuit fromgrounded battery through the righthand winding of relay 309, frontcontact and inner armature of relay 305, front contact and outerarmature of relay 304, conductor 223, terminal 218} brush 261 and thenceover the circuiflpreviously traced through the apparatiis at substationA, and back through brush 26(), terminal 217, conductor 224, innerarmature and front contact of relay 304, outer armature and frontcontact ofrelay 305 through the left-hand winding of relay 309 toground. Relay 309 at its right-hand armature completes a circuit to holdup slow-to-release relay 302 when sl'ow-to-release relay 325 isdeenergized due to the retraction of the outer right-hand armature ofrelay 308. In attracting its left-hand armature, relay 309 operatescentral ofiice line, relay 314 to light the call lamp L in i the mannerpreviously described. The operator again inserts her plug 315 in jack316 thereby operating relay 311 over the circuit previously traced.Relay 311 in attracting its armature completes a circuit for relay 308which attracts its armatures to cut-off relay 305. Relay 305 in beingdeenergized completes the previously traced talking circuit betweensubstation A and the central ofiice.

In casethe subscriber at station A did not desire any central ofliceconnection, he would leave his receiver on its switchhook, so that nocircuit would be completed for relay 309, and shortly after thedeenergization of relay 308, relay 325 would retract its armature toopen the circuit of relay 302. Relay 302 in being deenergized removesfrom conductor 222 the ground which has been holding up relays 255, 273,277, 231, 171, 107 and 120. Relays 255, 171 and 120 in being deenergizcdcause the release, respectively, of the companion final switch 20, theselector switch 200 and the line finder switch 100, in the mannerdescribed for the release of connection between substations A and C, andthe system is now in normal condition ready for other calls.

Establishment of a call from the central 077506 to the private branchemclumge.

On calls from the central oflice to the private branch exchange, theoperator inserts her plug 315 in a jack 316 of an idle trunk circ'uitleading to the private branch exchange. A circuit is thereupon completedfrom grounded battery through the lower left-hand winding of repeatingcoil 318, supervisory relay 319, ring 320, spring 321, conductor 312,winding of relay 311, conductor 317, left-hand armature and back contactof relay 308, through the winding of re'ay 330, conductors 353 and 328,spring 329, tip of lug 315 through the upper lefthand win ing ofrepeating coil 318' to winding of relay 301, conductor 222, front, 1

contact and left-hand armature of relay 302 to ground. Relay 301 inattracting its right-hand armature closes a circuit from ground,right-hand armature and front contact of relay 301, conductor 331,armature and back contact of magnet 332, side switch arm 333, firstposition, through the lefthand winding of relay 334, arm 335, first"position, conductor 336 through the ri hthand winding of relay 334 togrounded attery.; Relay 334 is energized in this circuit and locksupfrom grounded battery through its right-hand winding, conductor 336,arm 335, first position, 1eft-hand winding front contact and armature ofrelay 334, back contact and armature of magnet 332, and conductor 331 toground at the right-hand armature of relay 301. Belay 302 in applyingground to conductor 222 also renders multiple terminals 219 of thistrunk line busy.

After the operator inserts her plug 315 in the jack of the trunk line,ringing current is impressed on the calledlinefrom a source of ringingcurrent (not shown),

through ring 320, spring 321, conductor 312,

winding of relay 311, inner left-hand armature and back contact of relay3 24, condenser 337, back contact and outer left-hand armature of relay324, conductor 328, spring 329, tip of plug 315, upper left-hand windingof repeating. coil 318 to ground. As the resistance of this path is low,relay 311 is energized to operate relay 308. Relay 308 in attracting itsarniatures completes a circuit from ground, front contact and innerright-hand armature or relay 308,

through the winding of relay 324 to grounded battery. A circuit isthereupon completed from grounded battery through relay 302 beingslow-to-release remained up until its substitute circuit was completed.Relay 338 in being energized completes a locking circuit for itself fromgrounded battery through its winding, left-hand armature and frontcontact to ground at the right-hand armature of relay 30 2. Relay 324 islocked up over a circuit from grounded batter through its winding, frontcontact and right-hand armature and conductor 306 to ground at theright-hand armature and front contact of relay 338. In attracting itsleft-hand armatures, relay 324 interrupted the ringing current circuitto cause relay 311 to be deenergized, thereby breaking the circuit ofrelay 308, which in retracting its armatures completes the previouslytraced circuit for relay 330, and opens the circuit of relay 325. Relay302 is held up by ground at the armature of relay 330 and relay 338 isheld up over its locking circuit after relay 325 retracts its armature.In retracting its outer right hand armature relay 308 completed anenergizing circuit for relay 305 which may be traced from groundedbattery through .the winding of relay 305, back contact and outerrighthand armature of relay 308, conductors 307 and 306, and theright-hand armature and' front contact of relay 338, to ground.

In attractin its right-hand armature, relay 338 comp eted a circuit fromground, front contact and right-hand armature of relay 338, left-handarmature and back contact of relay 303, conductor 339, arm 340,

first position, right-hand armature and back contact of relay 341, backcontact and armature of magnet 342 through the winding of said magnet togrounded battery. Magnet 342 makes and breaks this circuit at itsarmature and back contact and steps the brushes of the hunting switch 30over the terminals leading to receiving subscribers stations. Busyterminals are denoted by ground on sleeve terminal 343 which shunts theright-hand winding of relay 341. When an idle terminal is reached, acircuit is completed from grounded battery through both windings ofcut-off rel-a 344, terminal 343, brush 345, right-hand Winding of relay341, arm 340, first position, conductor 339, back contact and left-handarmature of relay 303 to ground at the right-hand armature and frontcontact of relay 338. Relay 341 attracts its armatures, at itsright-hand armature opening the circuit of magnet 342 to stop the switch30 on an idle set of terminals, and applying ground from the frontcontact and right-hand armature of relay 338 to test terminal 343 toprovide a busy test. At its left-hand armature relay 341 completes acircuit from grounded battery through the winding of relay 346,left-hand winding, front contact and armature of relay 341, and thencein parallel with the circuit of relay 344 to ground at' the right-handarmature of relay 338. Relay 346 is energized in this circuit and rela341 is held up after its right hand win ing has been shunted. Relay 346in attracting its righthand armatures, completes a circuit from a sourceof ringing current through the righthand winding of relay 347, backcontact and inner right-hand armature of said relay, front contact andinner right-hand armature of relay 346, brush 348, terminal 349 throughthe left-hand winding of relay 326, condenser 350, terminal 351, brush352, outer right-hand armature and front contact of relay 346, outerright-hand armature and back contact of relay 347 to ground.

Relay 347 is marginal and will not be energized in this circuit at thistime. Relay 326 however attracts its armature completing a circuit fromgrounded batter through lamp 354, right-hand winding, ront eontaet andarmature of relay 326, normal contact of answering key 327, to ground.Lamp 354 lights and informs the reeeivin subscriber that a call isawaiting attention on his associated line. The receiving subscriberthereupon throws his answering key 327, breaking the circuit for lamp354 which goes out. In operatingthe answering key a low resistanceshuntcircuit is completed in parallel with the circuit through the lefthandwinding of relay 326 and relay 347 is now energized. In attracting itsleft-hand armature, relay 347 completes a locking circuit for itself,while in attracting its righthand armatures relay 347 interrupts theringin circuit and closes a circuit for relay 309, w ich may be tracedfrom grounded battery through the right-hand winding of relay 309, frontcontact and inner armature of relay 305, conductor 356, relay 357,spring 359 of relay 358, front contact and 1nner right-hand armature ofrelay 347, front contact and inner right-hand armature of relay 346,brush 348, terminal 349, lowest spring of key 327, through the apparatusat substation F, top spring of key 327 terminal 351, brush 352, outerright-hand armature and front contact of relay 346, outer righthandarmature and front contact of relay 347, inner left-hand armature andback contact of relay'358, outer armature and front contact of relay305, through the left-hand winding of relay 309 to ground. Relay 309 isenergized and in attracting its left-hand armature completes a circuitfrom grounded battery, through the lower left-hand winding of repeatingcoil 318, winding of relay 319, ring 320, spring 321 conductor 312,winding of relay 311, conductors 317 and 310, front contact andleft-hand armature of relay 309 to ground. Relays 3'19 and 311 areenergized in this circuit, relay 319 0 erating its associatedsupervisory lamp not shown) to inform the central oflice operator thatthe call has been answered, and relay

